fbcode_builder: getdeps: add run_cmd() function

Summary:
This runs a command, raising an exception if it exits with a non-zero error status.

It prints out the arguments in a mostly copy-and-pasteable form, with PATH-like
env vars pretty printed to make it easier to see what is being invoked; here's
an example of how cmake is being invoked later in this stack:

```
 ---
+ CMAKE_PREFIX_PATH=\
+      /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/ninja-5d7ec7:\
+      /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/cmake-91dc9a:\
+ PKG_CONFIG_PATH=\
+      /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/ninja-5d7ec7/lib/pkgconfig:\
+      /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/cmake-91dc9a/lib/pkgconfig:\
+ cd /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/build/zstd-470344 && \
+ cmake configure /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/repos/github.com-facebook-zstd.git/build/cmake -DCMAKE_INST
ALL_PREFIX=/data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/zstd-470344 -DBUILD_SHARED_LIBS=OFF -DCMAKE_BUILD_TYPE=R
elWithDebInfo -G Ninja
```

Reviewed By: simpkins

Differential Revision: D14690999

fbshipit-source-id: cdb0c681c7dfdfdc6e8c96bf4830bfbcf666411b

build/fbcode_builder/getdeps/runcmd.py

@@ -0,0 +1,87 @@
+# Copyright (c) 2019-present, Facebook, Inc.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree. An additional grant
+# of patent rights can be found in the PATENTS file in the same directory.
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import os
+import subprocess
+
+from .envfuncs import Env
+from .platform import is_windows
+
+
+try:
+    from shlex import quote as shellquote
+except ImportError:
+    from pipes import quote as shellquote
+
+
+class RunCommandError(Exception):
+    pass
+
+
+def _print_env_diff(env):
+    current_keys = set(os.environ.keys())
+    wanted_env = set(env.keys())
+
+    unset_keys = current_keys.difference(wanted_env)
+    for k in sorted(unset_keys):
+        print("+ unset %s" % k)
+
+    added_keys = wanted_env.difference(current_keys)
+    for k in wanted_env.intersection(current_keys):
+        if os.environ[k] != env[k]:
+            added_keys.add(k)
+
+    for k in sorted(added_keys):
+        if ("PATH" in k) and (os.pathsep in env[k]):
+            print("+ %s=\\" % k)
+            for elem in env[k].split(os.pathsep):
+                print("+      %s%s\\" % (shellquote(elem), os.pathsep))
+        else:
+            print("+ %s=%s \\" % (k, shellquote(env[k])))
+
+
+def run_cmd(cmd, env=None, cwd=None, allow_fail=False):
+    print("---")
+    try:
+        cmd_str = " \\\n+      ".join(shellquote(arg) for arg in cmd)
+    except TypeError:
+        # eg: one of the elements is None
+        raise RunCommandError("problem quoting cmd: %r" % cmd)
+
+    if env:
+        assert isinstance(env, Env)
+        _print_env_diff(env)
+
+        # Convert from our Env type to a regular dict.
+        # This is needed because python3 looks up b'PATH' and 'PATH'
+        # and emits an error if both are present.  In our Env type
+        # we'll return the same value for both requests, but we don't
+        # have duplicate potentially conflicting values which is the
+        # spirit of the check.
+        env = dict(env.items())
+
+    if cwd:
+        print("+ cd %s && \\" % shellquote(cwd))
+        # Our long path escape sequence may confuse cmd.exe, so if the cwd
+        # is short enough, strip that off.
+        if is_windows() and (len(cwd) < 250) and cwd.startswith("\\\\?\\"):
+            cwd = cwd[4:]
+
+    print("+ %s" % cmd_str)
+
+    if allow_fail:
+        return subprocess.call(cmd, env=env, cwd=cwd)
+
+    try:
+        return subprocess.check_call(cmd, env=env, cwd=cwd)
+    except (TypeError, ValueError, OSError) as exc:
+        raise RunCommandError(
+            "%s while running `%s` with env=%r\nos.environ=%r"
+            % (str(exc), cmd_str, env, os.environ)
+        )